As a road bike guy from way back I can add that a quality bike and it’s components makes all the difference in the world. And lighter is better. I can’t tell you the difference the first time I bought my first Trek (back when the model was 100, 200 tells you how old I am). Buying from a Bike Shop is recommended if it’s your first because they can fit the bike to you. And no, the “Schwinn” at Wal Mart isn’t just like the one you had as a kid. Wal Mart just bought the name from a bankruptcy court

The chart is mostly accurate but is too generous at what types of surfaces road bikes can handle.

I ride my road bike 2000-2500 miles a year (which is a lot by some standards, and not much by others), and can honestly say I would not be comfortable riding it on gravel or dirt roads any distance more than a few feet. And I've moved up to 28mm tires, too. That's about as large as can possibly fit on your typical road bike.

Cyclocross bikes, and Touring bikes can often take wider tires, and would be more appropriate for surfaces as bad as dirt and gravel. Typical road bikes will be almost unmanageable on dirt and gravel, though.

For road+dirt+gravel, you'll want a bike that can accommodate 32mm to 42mm tires. For dirt+gravel+rough, 38 to 48mm. ...and it goes up from there as conditions worsen.

On the other end of the spectrum, you really don't want to be riding a 48mm knobby tire on the road. That hum you hear as a mountain bike whizzes by on a paved surface is the knobs on the tires providing rolling resistance (making it harder to maintain speed over distances), while the road simultaneously wears the knobs off the tires.